The present invention relates to a resist material used in the production of semiconductor devices and a pattern forming method using such a resist material. More particularly, the invention pertains to a resist material used for forming positive patterns with ultraviolet light, especially deep ultraviolet light with a wavelength of 300 nm or less, for example, KrF excimer laser light used as exposure energy source.
With a recent trend toward high-density integration of semiconductor devices, there has been rising call for shortening of wavelength of the energy source of exposure means used for fine working, particularly photolithography, and now use of deep ultraviolet light (300 nm or less) and KrF excimer laser light (248.4 nm) is seriously considered. However, there has yet been available no high-utility resist material suited for working with light with said range of wavelength.
Dissolution-inhibiting type resist materials comprising a polymer with high permeability to light with a wavelength of around 248.4 nm and a photo-sensitive compound having a diazodiketo group in the molecule have been developed as resist material for pattern formation using KrF excimer laser light or deep ultraviolet light as light source (Japanese Patent Application Kokai (Laid-Open) No. (JP-A-) 1-80944; JP-A-1-154048; JP-A-1-155338; JP-A-1-155339; JP-A-1-188852; Y. Tani et at: Proc. SPIE, 1086, 22 (1989), etc.). These dissolution-inhibiting type resist materials, however, are all low in sensitivity and unusable for applications involving use of deep ultraviolet light or KrF excimer laser light where a high-sensitivity resist material is required. Recently, as means for reducing the amount of energy required for exposure (means for elevating sensitivity), use of a chemically amplified resist material with an exposure-generated acid applied as medium has been proposed [H. Ito et al: Polym. Eng. Sci., 23, 1012 (1983)], and many reports on this type of resist material have been made public (U.S. Pat. No. 4,491,628 (1985) to H. Ito et al; JP-A-2-27660; U.S. Pat. No. 4,603,101 (1986) to J. C. Crivello et al; JP-A-62-115440; W. R. Brunsvolt et al: Proc. SPIE, 1086, 357 (1989); T. X. Neenan et al: Proc. SPIE, 1086, 2 (1989); R. G. Tarascon et al: SPE Regional Conference Technical Papers, Ellenville, N.Y., p. 11, 1988; JP-A-2-25850; Y. Jian et al: Polym. Mater. Sci. & Eng., 66, 41 (1992), etc.). These known chemically amplified resist materials, however, also have varied problems in practical use depending on the type of the polymer used. For example, in case of using phenol ether type polymers such as poly(p-tert-butoxycarbonyloxystyrene), poly(p-tert-butoxystyrene), poly(p-tert-butoxycarbonyloxy-.alpha.-methylstyrene), poly(p-tert-butoxy-.alpha.-methylstyrene), poly(tert-butyl p-isopropenylphenoxy-acetate), poly(p-tert-butoxycarbonyloxystyrene/sulfone), poly(p-tetrahydropyranyloxystyrene), poly {p-(1-methoxyethoxy)styrene}, poly {p-(1-phenoxyethoxy)styrene} or the like, the produced resist material tends to cause film separation during development due to poor adhesion to the substrate, and such resist material also proves poor in heat resistance, making it unable to obtain a good pattern. In case of using a carboxylic acid type polymer such as poly(tert-butyl p-vinylbenzoate) or poly(tetrahydropyranyl p-vinylbenzoate), the produced resist material is found unsatisfactory in permeability to light with a wavelength around 248.4 nm due to the presence of benzoyl group and therefore has poor resolution. In the case of poly(tert-butyl methacrylate), there are the problems of unsatisfactory heat resistance, poor dry etch resistance.
Resist materials using silicon-containing polymers have also been disclosed (JP-B-3-44290, etc.), but use of such silicon-containing polymers, for instance, poly(p-trimethylsilyloxystyrene) or poly(p-tert-butyldimethylsilyloxystyrene), is encounted with the problems such as low sensitivity and impossibility to perfectly remove the resist material by ashing as it contains silicon. Thus, these resist materials are hardly capable of practical use.
More recently, as the chemically amplified resist materials freed of the defects mentioned above, there have been reported a resist material using poly(p-tert-butoxycarbonyloxystyrene/p-hydroxystyrene) (JP-A-2-209977; JP-A-3-206458), a resist material using poly(p-tetrahydropyranyloxystyrene/p-hydroxystyrene) (JP-A-2-19847; JP-A-2-161436; JP-A-3-83063) and a resist material using poly(p-tert-butoxystyrene/p-hydroxystyrene) [JP-A-2-62544; JP-A-4-211258 (U.S. Pat. No. 5,350,660)]. The resist materials using these polymers, however, involve the problem of delay time (the problem of change of pattern size or deformation during the period from resist coating till exposure or from exposure till heat treatment (PEB)) which is hotly discussed recently in practical application of resist materials.
Further, resist materials using the polymers having an acetal group or ketal group introduced as protective group have also been reported (JP-A-2-19847; JP-A-2-161436; JP-A-4-219757; JP-A-5-281745; JP-A-5-249682). However, the resist materials using these polymers, for example, poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene), poly(p-1-methoxyethoxystyrene/p-hydroxystyrene), poly(p-1-methoxy-1-methylethoxystyrene/p-hydroxystyrene), poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/methyl methacrylate) and poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/fumaronitrile) have the problems of poor storage stability, great deterioration of pattern size and shape on defocuing and small focus margin, so that it is difficult to form resist patterns with consistent stability by using these resist materials. They also involve the problems of formation of scums (non-dissolved portion at the time of development) and poor mask linearity. JP-A-3-282550 discloses a resist material comprising poly(1-methoxy-1-methylethoxystyrene/p-hydroxystyrene) and diphenyliodium salt, but this resist material has the problems of poor adhesiveness to the substrate and delay time in addition to the problems mentioned above. Resist materials using the polymers according to the present invention, for example, poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/p-tert-butoxystyrene) have also been reported (JP-A-6-194842). These resist materials, however, are all designed for use with electron rays, and if they are exposed to ultraviolet light, such as KrF excimer laser light, there arise such problems as imperfect resolution of the bottom portion (footing) of the pattern and formation of scums and consequent transfer of such scums to the pattern during etching.
As viewed above, the chemically amplified resist materials, although high in sensitivity as compared with the conventional resist materials, still have difficult problems such as poor heat resistance of polymers used therefor, imperfect adhesion to the substrate, insufficient transmittance to light with a wavelength around 248.4 nm, unsatisfactory resolving performance, change of pattern size or deterioration of pattern shape with time, poor storage stability, insufficient focus margin, unsatisfactory mask linearity, footing of the pattern and formation of scums, which discourage practical application of these resist materials. Thus, the appearance of a practical high-sensitivity resist material freed of the above-said problems has been desired.